Over 1.5 million living animal species have been described, of which around 1.05 million are insects, over 85,000 are molluscs, and around 65,000 are vertebrates. Animals form a clade, meaning that they arose from a single taika spinni common ancestor. Animals consume organic material, breathe oxygen, have muscle cells, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development.
- Most members of Medusozoa, including jellyfish and most hydrozoans, have a polyp form as well, but also have a motile medusae stage.
- The protozoa were later moved to the former kingdom Protista, leaving only the Metazoa as a synonym of Animalia.
- The digestive chamber has two openings, a mouth and an anus, and in the Nephrozoa there is an internal body cavity, a coelom or pseudocoelom.
- Despite their morphological dissimilarity with all other animals, genetic evidence suggests sponges may be more closely related to other animals than the comb jellies are.
- In carnivorous or omnivorous species, predation is a consumer–resource interaction where the predator feeds on another organism, its prey, who often evolves anti-predator adaptations to avoid being fed upon.
- Vertebrates such as the lobe-finned fish Tiktaalik started to move on to land in the late Devonian, about 375 million years ago.
Animals range in size from 8.5 millionths of a metre to 33.6 metres (110 ft) long and have complex interactions with each other and their environments, forming intricate food webs. A fish is adapted to its life in water and a crab is adapted to a life catching and eating insects. Animals that eat both plants and meat are called omnivores. Other animals eat only meat and are called carnivores. Some animals eat only plants; they are called herbivores.
Sponges lack the complex organisation found in most other animal phyla; their cells are differentiated, but in most cases not organised into distinct tissues, unlike all other animals. Despite their morphological dissimilarity with all other animals, genetic evidence suggests sponges may be more closely related to other animals than the comb jellies are. Sponges are physically very distinct from other animals, and were long thought to have diverged first, representing the oldest animal phylum and forming a sister clade to all other animals.
Ambulacraria are exclusively marine and include acorn worms, starfish, sea urchins, and sea cucumbers. Most protostomes have schizocoelous development, where cells simply fill in the interior of the gastrula to form the mesoderm. Many bilaterian phyla have primary larvae which swim with cilia and have an apical organ containing sensory cells.
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- The human population exploits a large number of other animal species for food, both of domesticated livestock species in animal husbandry and, mainly at sea, by hunting wild species.
- It first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm.
- Most protostomes have schizocoelous development, where cells simply fill in the interior of the gastrula to form the mesoderm.
- The protostomes include the Ecdysozoa, named after their shared trait of ecdysis, growth by moulting, Among the largest ecdysozoan phyla are the arthropods and the nematodes.
- Animals (or Metazoa) are living creatures with many cells that make up the kingdom Animalia.
- Animals are the sister group to the choanoflagellates, with which they form the Choanozoa.
- Most animals rely on biomass and bioenergy produced by plants and phytoplanktons (collectively called producers) through photosynthesis.
Everything you need to know about caring for dogs, cats, birds, fish, and exotic pets. Fresh content from wildlife researchers, zookeepers, and nature enthusiasts. EX Extinct EW Extinct in the Wild CR Critically Endangered EN Endangered VU Vulnerable NT Near Threatened LC Least Concern Oak Toad Oarfish Ocean Perch Ocean Pout Ocean Whitefish Oceanic Whitetip Shark Ocellated Turkey Ocelot Octopus Oenpelli python Oilfish Okapi Old English Sheepdog Old House Borer Oleander Hawk Moth Olingo Olive Baboon Olive python Olive Sea Snake Olm Olympic Marmot Onagadori Chicken Onager Opabinia Opah Opaleye (Rudderfish) Opossum Oranda Goldfish Orange Baboon Tarantula Orange Dream Ball Python Orange Roughy Orange Spider Orange Tanager (Orange-Headed Tanager) Orange-Crowned Warbler Orangutan Orb Weaver Orchard Oriole Orchid Dottyback Oregon Spotted Frog Ori-Pei Oribi Oriental Cockroach Oriental Dwarf Kingfisher Orinoco Crocodile Ornate Bichir Ornate Black-Tailed Rattlesnake Ornate Box Turtle Ornithocheirus Ornithomimus Ortolan Bunting Oscar Fish Osprey Ostracod Ostrich Otter Otterhound Ovenbird Oviraptor Owl Owl Butterfly Owlfly (Ascalaphidae) Ox Oxpecker Oyster Oyster Toadfish Ozark Bass A wide variety of animals are kept as pets, from invertebrates such as tarantulas, octopuses, and praying mantises, reptiles such as snakes and chameleons, and birds including canaries, parakeets, and parrots all finding a place.
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The Porifera (sponges) have long been assumed to be sister to the rest of the animals, but there is evidence that the Ctenophora may be in that position. Animals are the sister group to the choanoflagellates, with which they form the Choanozoa. It is thought to be one of the earliest predators, catching small prey with its nematocysts as modern cnidarians do.
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The apparent suddenness of the event may however be an artefact of the fossil record, rather than showing that all these animals appeared simultaneously. Analyses of pelagophyte algae consistently recover a Phanerozoic origin, while analyses of sponges recover a Neoproterozoic origin, consistent with the appearance of 24-ipc in the fossil record. Its likely origin is from sponges based on molecular clock estimates for the origin of 24-ipc production in both groups. 24-Isopropylcholestane (24-ipc) has been found in rocks from roughly 650 million years ago; it is only produced by sponges and pelagophyte algae. Species estimates shown here are based on numbers described scientifically; much larger estimates have been calculated based on various means of prediction, and these can vary wildly.
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The protostomes include the Ecdysozoa, named after their shared trait of ecdysis, growth by moulting, Among the largest ecdysozoan phyla are the arthropods and the nematodes. In deuterostomes, the mesoderm forms by enterocoelic pouching, through invagination of the endoderm. In deuterostomes, the anus forms first while the mouth develops secondarily. Animals from both groups possess a complete digestive tract, but in protostomes the first opening of the embryonic gut develops into the mouth, and the anus forms secondarily.
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Typically, there is an internal digestive chamber with either one opening (in Ctenophora, Cnidaria, and flatworms) or two openings (in most bilaterians). Non-human animals are also an important element of human culture, having appeared in cave arts and totems since the earliest times, and are frequently featured in mythology, religion, arts, literature, heraldry, politics, and sports. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa (now synonymous with Animalia) and the Protozoa, single-celled organisms no longer considered animals. Nearly all modern animal phyla first appeared in the fossil record as marine species during the Cambrian explosion, which began around 539 million years ago (Mya), and most classes during the Ordovician radiation 485.4 Mya. Animals first appeared in the fossil record in the late Cryogenian period and diversified in the subsequent Ediacaran period in what is known as the Avalon explosion. They have complex ecologies and interactions with each other and their environments, forming intricate food webs.
The blue whale (Balaenoptera musculus) is the largest animal that has ever lived, weighing up to 190 tonnes and measuring up to 33.6 metres (110 ft) long. Vertebrates such as the lobe-finned fish Tiktaalik started to move on to land in the late Devonian, about 375 million years ago. Some benthic animals living close to hydrothermal vents and cold seeps on the dark sea floor consume organic matter produced through chemosynthesis (via oxidising inorganic compounds such as hydrogen sulfide) by archaea and bacteria. Most animals rely on biomass and bioenergy produced by plants and phytoplanktons (collectively called producers) through photosynthesis. Selective pressures imposed on one another lead to an evolutionary arms race between predator and prey, resulting in various antagonistic/competitive coevolutions. In carnivorous or omnivorous species, predation is a consumer–resource interaction where the predator feeds on another organism, its prey, who often evolves anti-predator adaptations to avoid being fed upon.
